Default or optional Parameters in C#

[Spectre_001]

Not exactly elegant but...

public static void sample(int i, string s, bool b)
{
if (i == default(int)) { i = 100; }
if (s == default(string)) { s = string.Empty; }
if (b == default(bool)) { b = true; }

// The rest of your method...

}

Works in .NET Framework 3.5.

Kevin Rucker, Application Programmer QSS Group, Inc. United States Coast Guard OSC Kevin.D.Rucker@uscg.mil "Programming is an art form that fights back." -- Chad Hower

[PIEBALDconsult]

C# 4 !

[Hari Om Prakash Sharma]

visual studio 2010

First and the Foremost: FIGHT TO WIN

[hground]

VB .NET has had optional parameters for some time :) Looks like it took C# a while to catch up :) (Yeah - I know! I shouldn't throw rocks at hornet's nests, but sometimes you just can't resist!)

[jlafay]

That's possible in C# 4, and the same syntax applies. -jeff

[grgran]

As already pointed out, optional, default and named parameters are available in .NET 4.0 Interestingly, if you do use them the code analysis tool slaps your hand about it, requesting that you create overloads with the defaults set in method. G

[Paladin2000]

No, you can't set default values. But you can use an overload to accomplish something similar.

public static void sample(int i, string s, bool b)
{
///Something
}

public static void sample()
{
sample(100, string.Empty, true);
}

public static void sample(int i)
{
sample(i, string.Empty, true);
}

///Etc...

[djdanlib 0]

Wait, how does that even work? I've never even heard of something like that. I am intrigued. Is this what you're doing? http://msdn.microsoft.com/en-us/library/xwth0h0d%28v=VS.80%29.aspx[^]

[Spectre_001]

Yes, it just returns the framework's default value for the type specified.

Kevin Rucker, Application Programmer QSS Group, Inc. United States Coast Guard OSC Kevin.D.Rucker@uscg.mil "Programming is an art form that fights back." -- Chad Hower

[Fabio Franco]

LOL, please say it again, just one more time :laugh:

[PIEBALDconsult]

grgran wrote:

.NET 4.0

C# 4 dagnabit!!!

[PIEBALDconsult]

Done, but I've now run out of attributes -- how do you do blinking?

[PIEBALDconsult]

So, then, how would I specify 0, null, and false (?) when I want to?

[StephenPhillips]

Hmm, surely that misses the advantage of giving optional parameters, i.e. you can call the function without specifying all the input - using this form means you still need to give three values, or it doesn't match the function. Also, in this example, it's impossible to supply 'false' for the third value; false is the default value for a bool, so it would always become true.

[Jeff Connelly]

Yes, the C# lost that feature from "primitive" C++. You get it back with interest in C# 4.0 - not only can you provide default parameter values, you can also name your parameters and provide them in any order you want. For example, in C++ you had to order your function parameters correctly, so that the ones with default values came at the end. void foo(int i = 1, int j = 0, int k) This didn't work, because what does the call foo(1, 2) mean? In C# 4.0, you can do that. foo(k: 0, j: 1) So add "named" parameters (arguments) to the feature, which was not available in C++.

[Spectre_001]

You're absolutely correct, the only way to truly emulate optional parameters like in VB would be to use overloads of the method like this:

public static void sample(int i, string s, bool b)
{
// Do work here
}

public static void sample(int i)
{
sample(i, string.Empty, true);
}

public static void sample(int i, string s)
{
sample(i, s, true);
}

public static void sample(int i, bool b)
{
sample(i, string.Empty, b);
}

public static void sample(string s)
{
sample(100, s, true);
}

public static void sample(string s, bool b)
{
sample(100, s, b);
}

public static void sample (bool b)
{
sample(100, string.Empty, b);
}

public static void sample()
{
sample(100, string.Empty, true);
}

Which swiftly becomes unweildy once you get past three parameters.

Kevin Rucker, Application Programmer QSS Group, Inc. United States Coast Guard OSC Kevin.D.Rucker@uscg.mil "Programming is an art form that fights back." -- Chad Hower

[Spectre_001]

See the answer I posted to StephenPhillips.

Kevin Rucker, Application Programmer QSS Group, Inc. United States Coast Guard OSC Kevin.D.Rucker@uscg.mil "Programming is an art form that fights back." -- Chad Hower

[ely_bob]

This is what I use, however I'll admit I feel it slopifies the code base.... :doh:

I'd blame it on the Brain farts.. But let's be honest, it really is more like a Methane factory between my ears some days then it is anything else...
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"The conversations he was having with himself were becoming ominous."-.. On the radio...